ABSTRACT
Background: Regular physical activity is prime modality for the prevention of numerous non-communicable diseases and has also been advocated for resilience against COVID-19 and other infectious diseases. However, there is currently no systematic and quantitative evidence synthesis of the association between habitual physical activity and the strength of human immune system. Methods: We conducted systemic review and meta-analysis according to PRISMA guidelines and following a pre-registered protocol (PROSPERO CRD42020178825 ). We searched seven databases (MEDLINE, Embase, Cochrane CENTRAL, Web of Science, CINAHL, PsycINFO, and SportDiscus) up to April 2020 for randomised control trials and prospective observational studies were included if they compared groups of adults with different levels of physical activity and reported immune system cell count, concentration of antibody, risk of clinically diagnosed infections, risk of hospitalisation and mortality due to infectious disease. Studies involving elite athletes were excluded. The quality of the selected studies was critically examined following the Cochrane guidelines using ROB2 and ROBINS_E. Data were pooled using a random-effects model. Findings: A total of 16833 abstract were screened to identify 55 studies including seven prospective studies and 48 randomised control trials. The meta-analysis showed that higher level of habitual physical activity is associated with a 31% risk reduction (HR= 0.69 CI [0.61 – 0.78]) of community acquired infectious disease and 37% risk reduction (HR= 0.64 CI [0.59 – 0.70]) of infectious disease mortality. Randomised control trials showed that physical activity interventions resulted in increased immunosurveillance cell counts (CD4+, 32 cells/µL, 95% CI 7 to 56 cells/µL), increased immunoglobulin IgA concentration (standardised mean difference 0.311, 95% CI 0.131 to 0.484) and decreased neutrophil counts (704 cells/µL, 95% CI 68 to 1340) compared to inactive controls. Physical activity increased antibody concentration after vaccination compared to vaccination without adjunct physical activity (standardised mean difference 0.210, 95% CI 0.015 to 0.406). Results differed between healthy adults, obese adults, clinical population and older adults. There appear to be no moderating effects of physical activity volume, intensity or type.Interpretation: The practice of any type of regular, moderate to vigorous physical activity appears to be associated with enhanced immunosurveillance and mucosal immune responses. This is likely to explain the significant risk reduction of community acquired infectious diseases and infectious disease mortality, as well as an increase in the potency of vaccination.Funding Statement: None.Declaration of Interests: None.